1. Field of the Invention
This invention relates to a system for cooling, positioning and supporting electronic modules and, more specifically, but not limited to, such a system for use in conjunction with phased array microwave modules, primarily for use in phased array radar.
2. Brief Description of the Prior Art
A phased array radar system is formed from many transmit receive (T/R) microwave modules, one or more such modules being disposed in one or more apertures. One of the most critical problems in design and operation of a phased array system and particularly an airborne phased array system is the removal of heat from the modules within the aperture or apertures.
The modules dissipate a large amount of heat in a small volume. In order to maintain high system reliability, the heat dissipated by the modules must be removed while maintaining low component temperatures inside the modules. Also, since the microwave devices and circuits within the modules are temperature sensitive, low temperature gradients from module to module within the aperture and/or from aperture to aperture must be maintained. In addition, to assist in system start up, the thermal control system must also be capable of accommodating additional heat for system warm-up at start-up.
The system must be low cost, light weight, small in volume and consume a minimum amount of power. It must also fit into the physical constraints imposed by the module, aperture and vehicle for which the phased array system is configured. Sufficient room must be provided inside the modules to mount the circuits. The thermal, mechanical and structural system must not interfere with DC, RF and logic signal distribution circuits, electrical connectors, antenna elements, module tie down or module removal.
In one prior art approach to the above noted problems, air is blown between spaced apart modules and provides convection cooling between modules and the air stream. This cools the module cover and the devices inside the module which are linked to the cover through a conductive thermal path within the module. The cooling air is supplied to the modules by air ducts at the end of the air passages. This design is simple and light weight, however it is limited to modules with very low heat dissipations because of the large convective temperature rise and amount of power required to supply the large volume of air needed. The large air requirement handicaps the aircraft because the air must be delivered to remote parts of the aircraft. Air cooling also makes temperature gradient control and warm-up of the modules very difficult.
In a further prior art device, each module is mounted on a coldplate containing a circulating cooling fluid. The microwave circuits are mounted on the surface which will contact the coldplate, resulting in a small temperature rise from the fluid to the circuits. This system has the disadvantage of reduced maintainability since it is necessary to remove an entire row of modules to service a single module. The coldplate also adds extra weight to the system. All liquid systems will require an external heat exchanger and pump. This sacrifice must be made in order to cool high heat dissipation modules. The above described prior art is discussed in Haws, J. L., "Phased Array Thermal Control System Concepts", Proceedings Of The International Symposium On Cooling Technology For Electronic Equipment, March, 1987, Page 138.
A still further prior art thermal control system utilizes heat pipes and is an acceptable design approach, though it has some significant disadvantages. The disadvantages are in the areas of performance, cost and producibility. The heat pipes are costly to build because of their strict thermal performance requirements in a dynamic environment (i.e., they are sensitive to gravity changes, such as the aircraft acceleration, which has a drastic impact on the thermal performance of the heat pipes). The heat pipes are perpendicular to the center lines of the modules and the energy emanating from the modules is perpendicular to the heat pipes. Accordingly, during maneuvering of the aircraft, the heat pipe function can be lost completely or at least partially impaired. The heat pipes also impact the electrical performance of the phased array systems because the difference in thermal performance from heat pipe to heat pipe impacts the transmitted phase of the microwave modules. This system concept also requires a very complex and costly liquid cooled coldplate, making this approach undesirable. The above described prior art is discussed in Haws, J. L., "Phased Array Thermal Control System Concepts", Proceedings of the International Symposium on Cooling Technology for Electronic Equipment, March, 1987, Page 138.
A yet further prior art thermal control system as disclosed in U.S. Pat. No. 4,044,396 uses heat pipes which are positioned longitudinally relative to the modules and the long dimension of the aircraft and parallel to the direction in which heat is radiated out from the modules. In this arrangement, the failure of the heat pipes due to gravity forces is minimized. However, since heat pipes are required, the inherent problems associated with heat pipes as set forth hereinabove are present. The above cited publication further discusses such system.
It is therefore readily apparent that the prior art systems for cooling phased arrays of the type herein noted all have inherent undesirable limitations which should be minimized.